Device for clamping sheet material



Oct. 27, 1970 P. STRAUBE 3,536,321

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United States Patent Office 3,536,321 Patented Oct. 27, 1970 3,536,321DEVICE FOR CLAMPING SHEET MATERIAL Peter Straube, Radebeul, Germany,assignor to VEB ruckmaschinenwerir Planeta, Radeheul, Germany Filed June13, 1968, Ser. No. 736,683 Int. Cl. B6511 /14; B41f 1/30 U.S. Cl. 271535 Claims ABSTRACT OF THE DISCLOSURE A gripping finger is first moved toa position above and substantially parallel with a stationary supportsurface upon which the sheet material is lying, and subsequently loweredin perpendicular direction to clamp the sheet material against thissupport surface.

BACKGROUND OF THE INVENTION The present invention relates to a devicefor clamping a sheet material between a stationary support and a movablegripping means.

In particular, the present invention relates to sheet processingmachines, such as printing machines for example, Where an extremelyaccurate positioning of sheets is necessary to insure the requiredaccuracy of printing. The devices for clamping of sheets must maintainexactly the same position of the sheet during the printing process asthat which has been originally set on the feeding devices. It isnecessary to apply considerable holding forces against the sheet and,consequently, great forces in bearings of the clamping mechanism willresult.

To reduce these bearing forces there have been known devices where thegripping finger is spring-supported upon a gripper body which, is movedon a circular path. One of the disadvantages of such known devicesresides in the fact that due to the circular movement of the resilientgripping finger the latter is tangentially displaced when contacting thesheet support surface and, therefore, an exact fixation of the sheet isimpossible.

It has already been proposed to avoid, at least in part, this latterdisadvantage of circular movements by arranging the trunnion for theresiliently supported gripping finger, the center point of the grippershaft and the contact point between the closed gripping finger and thesupport surface of the impression cylinder, to lie substantially in astraight line. The result of this measure is that the final phase of theclamping movement is approximately in the region of 90 at which thesinus function and, consequently, the displacement of the resilientgripping finger are substantially reduced.

However, even such a small displacement is disadvantageous when an exactfixation is required for the sheet passing through a number of sites oftransfer.

SUMMARY OF THE INVENTION It is accordingly a primary object of thepresent invention to provide exact fixation of the position of a sheet.

In particular, it is an object of the present invention to provide adevice which makes it possible to avoid relative traverse motionsbetween the clamping means.

In accordance with a primary feature of this invention, a control shaftis disposed for pivoting about an axis parallel to the front edge of asupport surface upon which the sheet material is positioned. The shaftis provided with with a radial pushing arm and a radial carrier arm.Upon the shaft, a slide collar is pivotably arranged. The slide collaris integral with a radial stop arm, a carrier pin and a traversebracket. Between the radial stop arm and a fixed point, a pulling springis provided for pivoting the slide collar and thereby the traversebracket in the direction towards said support surface. A fixed stopscrew is located in the path of movement of the radial stop arm to abutthe latter in an adjusted position of the slide collar. The carrier pinis adapted for engagement with the carrier arm when the drive shaftrotates in direction away from said support surface. The gripping meansconsists of a gripping finger attached to a support block. The supportblock is afiixed to a slide rod which is perpendicular to the traversebracket and passes through a guide sleeve mounted on this bracket. Thesupport block is further coupled to a number of leaf springs which arearranged in parallel relationship to the traverse bracket and keep thesupport block with the gripping finger in the proper position withrespect to the sheet support surface. A second spring is secured betweenthe traverse bracket and the lower portion of the slide rod and pushesthe latter downwardly so that in an unactuated position the supportblock is adjacent to the traverse bracket. The pushing arm is adapted tothrust the slide rod when the drive shaft rotates in the direction awayfrom the support surface. The position of the carrier arm is adjusted sothat it starts moving the slide collar after the slide rod and therebythe gripping finger has been lifted. For a proper operation of thedevice it is necessary that the first spring be stronger than saidsecond spring.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is illustrated by way ofexample in the accompanying drawings, in which:

FIG. 1 is a schematic illustration of the device according to thepresent invention having gripping means in an open position;

FIG. 2 is the device of FIG. 1 at the end of the first phase of theclamping movement;

FIG. 3 is the device of FIG. 2 with gripping means in a closed position;and

FIG. 4 is the device according to this invention mounted on animpression cylinder of a printing machine.

DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in FIGS. 1 to 4, theclamping device of this invention consists of a gripper control shaft 1which is mounted for rotation about its axis 19 in a recess 18a of animpression cylinder 18. The control shaft supports a slide collar 2 andis terminated at one end thereof with an adjustable clamp ring 11. Theslide collar 2 is integral with a traverse bracket 2a which at a certainangular position of the collar is parallel to a sheet support surface1817 on the impression cylinder. The collar 2 is further provided withan axially protruding carrier pin 16 and with a radial stop arm 9. Thetraverse bracket 2a carries gripping means which are guided for aslidable movement perpendicular to the traverse bracket. The grippingmeans consist of a gripping finger 4 attached to a gripper block 6 whichis afiixed to a slide rod 6a. The slide rod passes through a guidesleeve 13 and is provided with a push spring 12 which pushes the entiregripping means downwardly. The traverse bracket also supports a numberof leaf springs 5 which are mounted in parallel spaced relationship oneto another in a leaf spring block 3 and coupled to the gripper block 6to insure the exact orientation of the gripping finger 4 with respect tothe sheet.

A pull spring 8 is connected between a fixed point 14 on the cylinder 18and the radial stop arm 9 to pull the latter as far as to an adjustablestop screw 10 which defines the parallel position of the traversebracket 2a and thereby of the gripping finger 4 with respect to thesupport surface 181:.

The clamp ring 11 is provided with a radial carrier arm 11a whichengages the carrier pin 16, and with a radial pressure arm 11b whichactuates the slide rod 6a by engaging a foot 6b fixed on the rod 6a.

All movements of the gripping finger 4 (as designated by arrows in FIGS.1 to 3) are derived from pivotable movements of the control shaft 1. Torelease the gripping means, the control shaft rotates counterclockwiseas far as to an end position shown in FIG. 1. At the first phase of thiscounterclockwise movement (see FIG. 3), the pressure arm 11b first abutsthe slide rod 6a. Since the tension of the spring 12 is lower than thatof the spring 8, the pressure arm 11b pushes the slide rod upwardlywhile the slide collar 2 remains stationary. As a result, the grippingfinger 4 releases the sheet 17 in exactly perpendicular direction sothat no tangential displacement thereof can occur.

As soon as the gripping finger is in the elevated position above thesupport surface as shown in FIG. 2, the carrier arm 11a will engage thecarrier pin 16 and initiate a second phase of the movement by pivotingthe traverse bracket about the axis 19 until the end position of FIG. 1is attained.

The closing operation is carried out in opposite order by driving thecontrol shaft in clockwise direction. The perpendicular travel of thegripping means which in practice equals approximately a double thicknessof the clamped sheet material, may be adjusted by setting screw 20. Onthe other hand, the clamping force of the gripping finger against thesheet 17 is adjustable by means of the stop screw which permits the pullspring 8 to execute the so-called over-pressure phase of the clampingmotion.

What is claimed is:

1. A device for clamping a sheet material between a stationary supportsurface and a movable gripping means, comprising a drive member mountedfor pivoting about an axis parallel to the plane of the support surfacefrom a first position in which the sheet material is clamped between thegripping means and the support surface to a second position in which thegripping means is displaced further from the support surface along aline perpendicular to the support surface and finally to a thirdposition in which the gripping means is displaced furthest from thesupport surface and outside said line, a slide member freely mounted onthe drive member for pivoting about the axis, two leaf springs arrangedmutually parallel, parallel to the support surface and in a planetransverse to the axis, means rigidly fixing one end of each of the leafsprings to each other and to the slide member, connecting means rigidlyfixing the other end of each of the leaf springs to each other, saidgripping means being connected to the connecting means, means fordrivingly connecting the drive member with the slide member continuouslybetween the second position and the third position so that the drivemember pivots the slide member with the drive member and disconnectingthe drive member from the slide member continuously between the firstposition and the second position and means for drivingly'connecting thedrive member with the gripping means continuously between the firstposition and the second position.

2. A device according to claim 1, in which the means for drivinglyconnecting the drive member with the slide member comprises a pin on theslide member and an arm on the drive member, said arm being displacedfrom said pin when the drive member is between the first position andthe second position and being in engagement with said pin when the drivemember is between the second position and the third position.

3. A device according to claim 2, in which the means for drivinglyconnecting the drive member with the gripping means comprises a secondarm on the driving member, an elongated member, one end of the elongatedmember being fixed to the means connecting the other end of each of theleaf springs to each other and the other end of the elongated memberbeing in driven engagement with the second arm continuously between thefirst position and the second position.

4. A device according to claim 3, further comprising spring means oneend of which is fixed to supporting structure which is stationaryrelative to the support surface and the other end of which is fixed tothe slidable member so that the spring means is stressed as the slidablemember is driven from the second position to the third position.

5. A device according to claim 4, further comprising a bearing arm fixedto the slidable member, said bearing arm being transverse to andslidably supporting said elongated member, and second spring means, oneend of said second spring means being fixed to said other end of theelongated member and the other end of said second spring means beingfixed to said bearing arm so that the second spring means is stressed asthe slidable member is driven during the pivoting of the driven memberfrom the first position to the second position.

References Cited UNITED STATES PATENTS 549,282 11/1895 Wenot 101-4092,699,941 1/1955 Huck et a1 27153 2,865,289 12/1958 Fowlie et al.101-409 3,172,353 3/1965 Helms 10193 WILLIAM B. PENN, Primary ExaminerE. M. COVEN, Assistant Examiner US. Cl. X.R. 101-409

